The present invention relates to a variable displacement compressor capable of changing its displacement by changing the crank chamber pressure.
FIG. 5 shows a swash plate compressor to be used in a vehicle air conditioner. A crank chamber 82 is defined between a front housing 80 and a cylinder block 81. A drive shaft 83, which is driven by a vehicle engine, is supported by the crank chamber 82 and the cylinder block 81. The crank chamber 82 contains a lug plate 84 that rotates integrally with the drive shaft 83. A swash plate 85 is connected to the lug plate 84 through a hinge mechanism 102.
A plurality of cylinder bores 86 are defined in the cylinder block 81. Each cylinder bore 86 contains a piston 87. The drive shaft 83 rotates the swash plate 85 to make each piston 87 connected to the swash plate 85 reciprocate between a top dead center position and a bottom dead center position within the cylinder bores 86. The stroke of each piston 87 is changed depending on the inclination angle of the swash plate 85 to change the displacement of the compressor.
A valve plate 88 is located between the cylinder block 81 and a rear housing 89. The rear housing 89 contains a suction chamber 90 and a discharge chamber 91. As each piston 87 reciprocates, a refrigerant gas in the suction chamber 90 is caused to flow into the cylinder bore 86. After the refrigerant gas is compressed in the cylinder bore 86, it flows into the discharge chamber 91.
The inclination angle of the swash plate 85 is determined by controlling the internal pressure of the crank chamber 82 (crank chamber pressure) with an electromagnetic control valve 93. A supply passage 92 connects the discharge chamber 91 and the crank chamber 82 to each other through the electromagnetic control valve 93. The electromagnetic control valve 93 controls the quantity of refrigerant gas flowing into the crank chamber 82 through the supply passage 92. A bleed passage 94 connects the crank chamber 82 and the suction chamber 90 to each other. The refrigerant gas in the crank chamber 82 is allowed to flow into the suction chamber 90 through the bleed passage 94 constantly at a predetermined flow rate.
When no electric current is supplied to the control valve 93, the valve 93 opens fully. Thus, the refrigerant gas is introduced to the crank chamber 82 at the maximum flow rate through the supply passage 92. This increases the crank chamber pressure to cause the swash plate 85 to assume the minimum inclination angle. The control valve 93 closes when an electric current is supplied thereto, and the refrigerant gas cannot flow from the discharge chamber 91 into the crank chamber 82. This reduces the crank chamber pressure to cause the swash plate 85 to assume the maximum inclination angle.
The swash plate 85 assumes the maximum inclination angle and the minimum inclination angle when it abuts against the lug plate 84 and against a restriction ring 101 fixed to the drive shaft 83, respectively.
The clearance between the drive shaft 83 and the front housing 80 is sealed with a lip seal 95. The distal end of the drive shaft 83 protrudes outward through the housing. An electromagnetic clutch 96 is attached to that end of the drive shaft 83. The electromagnetic clutch 96 includes a fixed clutch disc 96c supported by the front housing 80, a movable clutch disc 96a fixed to the distal end of the drive shaft 83 to oppose the fixed clutch disc 96c, and an electromagnetic coil 96b for moving the movable clutch disc 96a. When an electric current is supplied to the electromagnetic coil 96b, the movable clutch disc 96a is brought into contact with the fixed clutch disc 96c to transmit the driving force of an engine E to the drive shaft 83.
A thrust bearing 97 is located between the lug plate 84 and the front housing 80. The inner end of the drive shaft 83 is inserted to an insertion hole 98 defined in the cylinder block 81 and is supported therein. The insertion hole 98 contains a support spring 100, which is a compression spring. The support spring 100 is located between a snap ring 99 contained in the insertion hole 98 and a thrust bearing 103 attached to the inner end of the drive shaft 83. The support spring 100 urges the drive shaft 83 axially forward with respect to the front housing 80 (leftward in FIG. 5). The support spring 100 controls axial backlash of the drive shaft 83.
When a power switch of the air conditioner is turned off or when the engine E is stopped, the supply of electric current to the electromagnetic clutch 96 and to the control valve 93 is interrupted. Thus, the control valve 93 opens fully to let the refrigerant gas flow through the supply passage 92 into the crank chamber 82. Here, the crank chamber pressure increases temporarily to an excessively high degree due to the abrupt inflow of the gas. The swash plate 85 having moved to the minimum inclination angle position (indicated by the chain double-dashed line in FIG. 5) is then pressed against the restriction ring 101 with an excessive force. As a result, the drive shaft 83 retracts along its axis against the force of the support spring 100.
The displacement of the compressor is sometimes minimized to reduce the load of the compressor applied to the engine E during acceleration of a vehicle. In this case, the refrigerant gas flows rapidly into the crank chamber 82 as soon as the control valve 93 opens fully, which increases the crank chamber pressure temporarily to an excessively high degree. Thus, the drive shaft 83 retracts axially.
The retraction of the drive shaft 83 moves the pistons 87 toward the valve plate 88. Thus, each piston 87 impinges upon the valve plate 88 at the top dead center position and causes hammering or vibration.
The retraction of the drive shaft 83 also moves the movable clutch disc 96a of the electromagnetic clutch 96 backward. This brings the movable clutch disc 96a into contact with the fixed clutch disc 96c, although the electromagnetic coil 96b is demagnetized. As a result, the two clutch discs 96a and 96c generate friction, abnormal noise and heat.
Further, if the drive shaft 83 retracts, the axial position of the drive shaft 83 changes with respect to the lip seal 95 held in the front housing 80. Normally, the drive shaft 83 is in contact with the lip seal 95 at a predetermined axial position. The drive shaft 83 has a foreign matter such as sludge deposited on its outer surface at a position spaced from the predetermined axial position. Therefore, if the axial position of the drive shaft 83 changes with respect to the lip seal 95, the sludge is caught between the lip seal 95 and the drive shaft 83. This lowers the sealing performance of the lip seal 95 and permits gas leakage from the crank chamber 82.
To solve the problems described above, it is possible to use a support spring 100 having a greater force so that the drive shaft 83 is not retracted by an excessively increased crank chamber pressure. In this case, however, excessive loads are applied to the thrust bearings 97 and 103, which causes power loss in the compressor.
It is an object of the present invention to provide a variable displacement compressor capable of preventing shifting of the drive shaft in the axial direction.
In order to attain the above object, the present invention provides a compressor capable of changing its displacement depending on the internal pressure of the crank chamber. The compressor has a housing. The housing contains a cylinder block and a valve plate to be connected to the cylinder block. The cylinder block contains cylinder bores and a supporting hole. A piston is housed in each cylinder bore to compress gas drawn into the cylinder bore through the valve plate. The compressed gas is discharged from the cylinder bore through the valve plate. A drive shaft supported in the housing has an end portion to be inserted into the supporting hole. A drive plate is connected operationally to the pistons to convert the rotation of the drive shaft into reciprocating motions of the pistons. The drive plate is supported on the drive shaft and can incline. The drive plate inclines between a maximum inclination angle position and a minimum inclination angle position depending on the internal pressure of the crank chamber. The inclination angle of the drive plate determines the piston stroke and the compressor displacement. A movable body is housed in the supporting hole to be able to move in the axial direction. The end portion of the drive shaft is supported in the cylinder block through the movable body. An urging member urges the movable body toward the drive plate to bring the former into abutment against the latter. The movable body moves along the axis of the drive shaft as the drive plate is inclined. When the drive plate is located at the minimum inclination angle position, the valve plate receives force from the drive plate through the movable body.